1. Technical Field
Embodiments of the present invention relate to a capacitive load driving circuit that supplies a drive signal to a capacitive load such as a piezoelectric element so as to drive the capacitive load. More particularly, embodiments of the invention relate to an ink jet printer that includes an actuator as a capacitive load and that performs a printing operation by supplying a drive signal to the actuator so as to eject ink or to a fluid ejecting apparatus that includes an actuator such as a capacitive load connected to a diaphragm and that supplies a drive signal to the actuator so as to eject fluid.
2. Related Art
For example, when a drive waveform signal having a predetermined voltage waveform is amplified by a digital power amplifier and is used as a drive signal of an actuator, which is a capacitive load, the drive waveform signal is pulse-modulated into a modulated signal by a modulator, the modulated signal is amplified in power into a power-amplified modulated signal by the digital power amplifier, and the power-amplified modulated signal is smoothed into a drive signal by a smoothing filter.
When the waveform of the drive signal is important, a feedback signal can be generated from the drive signal. The feedback signal is phase shifted from the drive signal and may precede the drive signal in phase. A differential value between the feedback signal and the drive waveform signal obtained from a subtractor may be input to the modulator. For example, in JP-A-2007-96364, by inserting a phase-preceding compensator into a feedback circuit of a drive signal, an attempt is made to compensate for the waveform of the drive signal without inserting a dumping resistor before or after a smoothing filter. The pulse-modulated frequency in the modulator is referred to as a modulation frequency or a carrier frequency.
When an actuator as a capacitive load is separated from a digital power amplifier, a wire in addition to a substrate interconnection is necessary between the actuator and the digital power amplifier. In this case, it is not realistic that the drive signal actually supplied to the actuator be fed back, because an individual wire is necessary and the like. Accordingly, for example, an inductor is disposed at an output terminal of the digital power amplifier and a signal at a connecting point between the inductor and the wire is fed back. However, when the input signal to the wire is fed back, signal amplitude in a modulation frequency band exceeding an operating range of the subtractor or the modulator may remain in a feedback signal when only the phase-preceding compensator is inserted into the feedback circuit. In this case, there is a problem because it is not possible to satisfactorily compensate for the drive signal.